The US Patent 2007/0205943 A1 and the IEEE 802.15.3c standard contributions “mm Wave Beam forming” and “mm Wave Multi-Resolution Beamforming” respectively propose beam forming methods whereby antenna training is achieved, by sending or receiving test signals, where for each test signal the phases of the phase shifters in the antenna array corresponds to a column or row of an unitary matrix. By sending or receiving sufficient test signals to cover all the rows or columns of the unitary matrix the receiver can calculate the optimum settings for the phase shifters. Such a calculation utilises the special properties of the unitary matrix which simplifies calculating the matrix inverse. An unitary matrix is an orthogonal matrix of a subset of beam positions, whereby the matrix is a complex matrix comprising complex values.
The IEEE 802.15.3c standard contributions “Robust and Highly Efficient Beamforming Procedures for 60 GHz WPAN˜Beam Searching and Tracking˜” and “Beamforming” propose a beam forming method which has multiple stages, whereby in each stage finer beam widths are used to send test sequences to determine the best transmitter/receiver beam combination. The first stage of the method therefore strives to determine from which sector the best antenna combination for the transmitter and receiver is located. Subsequent stages use this information to determine the search areas for finer and narrower beams.
A drawback of state of the art beam forming methods using the unitary matrix approach is, that for antenna arrangements which have a low number of antennas (e.g. less than 8), there are some issues with orthogonally of the rows and columns of the unitary matrix when some antenna elements are not functioning as expected.
Furthermore, if the link performance or quality of the selected beam forming arrangement degrades, there are no alternative arrangements provided by the unitary matrix approach.
Other drawbacks of state of the art beam forming methods are based on decreasing the beam width with each step:
First, for optimum performance in some situations, the best radiation pattern which leads to best link performance may not be one with only one angular peak, but maybe one with multiple angular peaks. An example of this is when the transmitter and receiver are located in a small room and the line of sight transmission path is blocked. In such a scenario, it may be advantageous to transmit the signal simultaneously via multiple separate walls, which requires a radiation pattern with multiple angular peaks. Due to the ‘zooming in’ aspect of this approach, only a beam with one angular peak can be selected with this approach.
Second, when the best optimum fine beam is located between two coarse beams, there will sometimes be an error in selecting the wrong coarse beam in an early step. This ultimately leads to a non optimum fine beam being selected in a subsequent steps and results in degraded link performance.
EP 189 2852 A1 discloses an approach to determine received beams by sending a number of test sequences corresponding to the number of fundamental beams.
At the end, it is an object of the present invention to reduce the required effort to calculate and acquire the best beam arrangement between a receiver and a transmitter.